The General Packet Radio Service (GPRS) has been developed for communicating efficiently data packets to and from mobile user equipment via a second generation mobile radio network such as the Global system for Mobiles (GSM) or a third generation mobile radio network such as the Universal Mobile Telecommunications System (UMTS). GPRS provides support for a packet-orientated service, which attempts to optimise network and radio resources for packet data communications such as for example Internet Packets (IP). The GPRS provides a logical architecture, which is related to the circuit switched architecture of the second or third generation mobile radio network.
Generally, the GPRS network will be connected to another packet data telecommunications network, which may also be connected to further packet data telecommunications network. The network to which the GPRS network is connected will be referred to in the following description as an external network. The GPRS network for communicating data between a mobile communications user equipment (UE) and the external network comprises: a gateway support node (GGSN) which provides an interface between the external network and the user equipment. The GPRS network also includes a service support node (SGSN) which is operable to control communication of data packets between the gateway support node and the user equipment using a radio network controller (RNC) which controls radio resources of the telecommunications network.
The Internet Protocol as developed by the Internet Engineering Task Force (IETF) has become a preferred way of communicating packet data via telecommunications networks. Whilst version 4 of the Internet Protocol (Ipv4) has been standardised and has been deployed in many fixed networks, version 6 of the Internet Protocol is being developed in order to provide improved facilities. Amongst these improvements is a facility to communicate internet packets to and from mobile nodes, which roam from a home network to foreign network during an IP session [1]. Generally, following a process known as route optimisation which will be described shortly, a source and a destination address in the header of IP data packets being set from and to a mobile node (MN) respectively will change as a result of the MN roaming to the foreign network.
The mobile node may communicate Internet packets with a correspondent node (CN) which is attached to a GPRS network. As a result the GGSN of the GPRS network must be arranged to route the internet packets via an appropriate bearer to the correspondent node, which itself may be mobile. If the mobile node roams to a foreign network mid-session then the GGSN must be arranged to route the internet packets to the correspondent node (mobile user equipment) via an appropriate bearer. The appropriate bearer will have been set up by the GGSN when a session initiation was established at a time when the mobile node was attached to its home network. As such the parameters for the bearer will have been established with reference to a home address of the mobile node as the source address. However as explained above, the source address in the header of the internet packets will change during the session from the home address of the mobile node, when attached to its home network, to a care-of-address after the mobile node roams to the foreign network. Without adaptation, the GGSN will therefore drop internet packets with the care-of-address of the mobile node as source address rather than routing the packets via the bearer established for the mobile node's home address to the correspondent node.
It has previously been proposed to provide a mobile node's home address in an extension header field known as the hop-by-hop field. As such the GGSN will be able to identify the appropriate bearer through which internet packets can be routed to a correspondent node (CN) attached to the GPRS network, because the mobile node's home address provides the source address with respect to which the appropriate bearer was set up. Generally, however there remains a technical problem to improve inter-working between the Internet Protocol, in particular but not exclusively Ipv6 and a packet radio system such as but not exclusively the GPRS.